Understanding frequency bands

In fundamental concepts of sound, we covered some basic concepts like wavelengths and frequencies.

Acoustic experts often use frequency bands in their studies.

For non-experts, understanding concepts like third-octave and octave frequency bands can be tricky.

If you find this concept challenging, worry not! Atelier Crescendo has crafted this post just for you.

Enjoy the read!

(See at the end the references used to confirm these  concepts)

 

Acoustic analysis 


Studying the acoustic performance of materials or the acoustic characteristics of sources/signals comes in different ways.

Frequently, acoustic experts use frequency bands for measurements or calculations.

Essentially, it is a method to reveal acoustic information across different frequency ranges.

Most commonly, frequency analysis occurs in:

  • octave bands 
  • third-octave bands

In third-octave bands, the precision/resolution is about three times higher than in octave bands.

The formula to obtain octave band values from third octave values depends on the acoustic metric you want to study.

What is an octave ?


An octave is an (key musical) interval, corresponding to doubling or halving frequency.

 

Example: from 125 Hz to 250 Hz is an octave, as is 20,000 Hz to 10,000 Hz.

 

Musicians often use the A note as the reference for tuning. The frequency of this note is 440 Hz.  The A note at the next octave is 880 Hz

 

 

Upper & higher frequency band limits

and band centre frequency  


When talking about bands, we must set their upper and lower frequency limits.

Also, in each band, there is a center, known as the band center frequency. It is the mean of the upper and lower limits.

 

Example: in the 250 Hz center frequency octave band:

  • the lower limit is 178 Hz
  • the upper limit is 355 Hz 

 

 

Setting limits for third-octave bands is a little more complex.

 

Preferred (and standardised) frequency bands


Frequency band analysis has even been standardised

International Standards Organisations have agreed on preferred frequency bands for the analysis of sound or vibrations.

Typically, in acoustic building projects, the frequency range under consideration spans from 63 Hz to 8000 Hz.

In the case of vibrations, exploration can extend to frequencies as low as 2 Hz.

Note: If you want to know about the standards, here they are: 

  • ANSI/ASA S1.6 (2020) – Preferred Frequencies And Filter Band Center Frequencies For Acoustical Measurements
  • ANSI/ASA 51.11 (2004) – Octave-Band And Fractional-Octave-Band Analog And Digital Filters
  • IEC 61260 -1 (2014) – Electroacoustics – Octave-band and fractional-octave-band filters – Part 1: Specifications
  • TS0 266 (1997)  – Acoustics – Preferred frequencies

 

References

See below the references used to confirm the above concepts:  

  • Noise Control in Building Services – Sound Research Laboratories Ltd – Pergamon Press
  • Sound Materials, A Compendium of Sound Absorbing Materials for Architecture and Design – Tyler Adams – Frame Publishers
  • Acoustic Absorbers and Diffusers – Theory, Design and Application – Third Edition –  Trevor Cox, Peter D’Antonio
  • Engineering Noise Control – Sixth Edition – CRC Press – David A. Bies, Colin H. Hansen, Carl Q. Howard, Kristy L. Hansen

 

Deep into wavelengths, frequencies and spectrums of instruments

 

This post is not very long.

It is a complement to the fundamental concepts of sound in which we explained about sound, sound waves, amplitude, wavelengths and frequencies.

Here, we firstly give you some ideas on the dimensions of wavelengths for different frequencies in the air. They are useful to know to better understand sound phenoma like: sound absorption, sound diffusion, sound diffraction and also sound transmission. 

Then we have included a graph with examples of spectrum of some instruments and sources. This way, you can visualise the frequencies they can emit. 

Wavelength dimensions


Below we illustrate wavelength dimensions for various frequencies within the audible range for humans.

These examples offer insights into the sizes of wavelengths associated with the sounds/frequencies we can hear.

 

 Note: We have approximated the wavelength values by calculating them under the assumption of air as the propagation medium, at a temperature of 20 degrees Celsius, resulting in a speed of sound at 343 meters per second.”

 

Examples of wavelength dimensions corresponding to different frequencies

Frequency

Corresponding Wavelength

20 Hz 

17,15 meters

50 Hz

6,86 meters

100 Hz

3,43 meters

500 Hz

69 cm

1000 Hz

34 cm

5000 Hz

6,9 cm

10000 Hz

3,4 cm

20000 Hz

1,7 cm

Examples of spectrums


Remember from the fundamental concepts of sound, “the natural sounds blend frequencies with varying amplitudes.” 

We call spectrum (in physical terms) the range of frequencies a source can emit.

Below we have included a graph with examples of spectrums of some instruments and sources. 

 

 

 

Fundamental concepts of sound

(Sound waves, amplitude, wavelength, frequency, etc)

Are you new to acoustics or need a refresher on sound basics?

This article was created to dive into the fundamental concepts of sound including:

 

  • Sound and sound waves
  • Sound wavelength
  • Sound amplitude
  • Sound frequency

 

Enjoy the read!

(See at the end the references used to confirm these  concepts)

 

Understanding sound and sound waves


Sound originates from vibrating objects in various mediums like solids, liquids, and gases.

These vibrations cause air particles to move back and forth, creating compression and rarefaction.

 

Compression occurs when particles bunch together, generating a higher pressure.

Conversely, rarefaction leads to lower pressure as particles spread apart.

These alternating pressure fluctuations give rise to the sounds we perceive.

These pressure variations form sound waves, classified as longitudinal waves because the air particles move in the same direction as the vibrations.

In air, sound waves travel at around 343 meters per second (at 20°C).

Understanding wavelength in sound waves


Wavelength in sound waves refers to the distance between two consecutive compressions or rarefactions of particules.

Typically, wavelengths are expressed in meters.

 

 

Understanding amplitude


Sound amplitude reflects the change in pressure from vibrations. Put simply, it relates the number of air particles involved in the vibration process.

A sound with a greater amplitude will be perceived as louder (or with a higher volume).

 

To measure amplitude, you use logarithmic decibels (dB).

For instance, a whisper might register around 30 dB, while a rock concert can reach a staggering 120 dB or higher.

Understanding frequencies 


Frequencies, measured in Hertz (Hz), directly relate to sound wave speed divided by the wavelength.

  • shorter wavelengths correspond to higher frequencies…

 

  • while larger wavelengths align with lower frequencies

Higher frequencies result in higher pitches, while lower frequencies create lower pitches. Listen below to some examples perfect pitches at different frequencies.

 

100 Hz pitch

500 Hz pitch

1000 Hz pitch

10000 Hz pitch

The audible range for most humans falls between 20 Hz to 20,000 Hz.

Natural sounds blend frequencies with varying amplitudes, forming a spectrum.

The unique timbre of sources, especially musical instruments, links closely to their individual spectra.

 

References

See below the references used to confirm the above concepts:  

  • Noise Control in Building Services  – Sound Research Laboratories (SRL) Ltd – Pergamon Press
  • Auditorium Acoustics and Architectural Design (Second Edition) – Michael Barron – Spon Press
  • Sound Materials, A Compendium of Sound Absorbing Materials for Architecture and Design – Tyler Adams – Frame Publishers

 

Noise and vibration challenges in sport, fitness and gym facilities

Part 2: Control of airborne noise

 

 

 

 

In sport, fitness and gym facilities, many activities and sources generate airborne noise including: 

 

  • Power amplified sound systems 
  • Exercise machines
  • Weights dropped (controlled or uncontrolled) on structures
  • People chatting, cheering, shouting, etc. 
  • Other noises specific to some sports (i.e. hockey, tennis, football, etc.)

 

This part explains the different paths of airborne noise transmission from the gym spaces to the adjacent/nearby noise sensitive receptors.

For each transmission path, it explains what happens and gives ideas of noise control solutions. 

 

Note 1: what is airborne noise exactly? go to this section  in part 1.

 Note 2 : read Who could the facility disturb iin part 1 to know what the noise sensitive receptors could be. 

 

 

 

Airborne noise transmission paths in sport, fitness and gym facilities

The main transmission paths of airborne noise are:

  • through the building façace.
  • through the internal building fabric and;
  • via the ventilation systems.  

It is also useful to control the sound reverberation in noisy spaces.

Follow the links to read what happens and know ideas of noise control solutions for each transmission path. 

 

Noise transfer through the building façade 

of sport, fitness and gym facilities

What happens?


 

 

In sport, fitness and gym facilities, activity and music noise:

 

  • transfers through the façade, 
  • and propagates through the air to the nearest sensitive receptor.

 

Local Authorities often ask to consider this aspect to make sure the new facility doesn’t cause an adverse impact on the neighbours

To do this, you need to undertake a noise impact assessment

 

Note: Most of the time, music and activity noise impact assessments aim to not exceed (to a degree) the existing noise environmental noise levels at the receptors. There are called subjective assessments’

But sometimes, undertaking a subjective assessment is not the most ‘reasonable’ approach

For very quiet sites, exceeding slightly the existing noise environmental noise levels may not cause an adverse impact.

In this case, undertaking an assessment based on not exceeding (again, to a degree) an objective requirement may be more appropriate. This requirement, usually from a guideline or a standard, has to be discussed and agreed with the Local Authority

You call such as assessment an ‘objective assessment’.

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What are the noise control solutions?


There are two main solutions to control music and activity noises in sport, fitness and gym facilities.

Solution 1:

Improve the façade elements and/or the roof

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You generally do it by creating cavities with dense & rigid board elements such as:

 

  • plasterboard lining on a frame with insulation in the cavity to improve the performance of the external walls.

You may need to decouple it from the rest of the building structure by introducing resilient fixings or, when possible, simply make the frame independant.

Examples of resilient fixings are resilient bars or resilient clips

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  • plasterboard ceiling on a frame with insulation in the cavity to improve the performance of the roof.

You may need to decouple it from the rest of the building structure by introducing resilient fixings.

As above, examples of resilient fixings are resilient  bars, clips or hangers.

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  • if the façade contains glazed elements, you may need to think about high performance double or triple glazing

Sometimes, secondary glazing is necessary when you need to increase the sound insulation performance at low frequencies.  

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Solution 2:

Install a noise limiter

 

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A noise limiter is usually a secondary solution. 

It is a device that limits (!!) the music levels emitted within a space to avoid too much noise spilling out of a facility. 

This way the music levels stay below certain thresholds at the nearest noise sensitive receptors. 

 

Note: the word thresholds here is with an “s” because you set the noise limiter in different frequency bands (or ranges).  

 

 

 Noise transfer through the internal building fabric 

of sport, fitness and gym facilities

What happens?


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In a building, the airborne noise transfers through the wall/floor constructions into adjacent spaces.

What are the noise control solutions?


Depending of the site and the context, you may have to implement some or all the following noise control solutions.

Solution 1:

Improve the floors

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You can improve the airborne sound insulation performance of a floor construction with:

 

  • a dense suspended ceiling that you decouple from the main structure with resilient fixings such as resilient bars, clips or hangers.

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Note: you may also need to consider a floating floor system in the gym. 

However, this is more to control the impacts of weights dropped and vibrations of some activities & equipment (see future parts on vibration isolation).

Solution 2:

Improve the walls

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You can improve the airborne sound insulation performance of external wall constructions in vary many different ways.  

However,  these two systems are recurrent when receptors are fairly close (< 20m) to the facilities :  

 

  • Drylining or ‘sandwichsystems. Most of the time, they include plasterboard on the indoor side. 

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  • Dense linings to masonry walls.

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For both methods, it might be useful to think about introducing:

 

  • a larger cavity to better control low frequency transmission. acoustics - acoustic design - airborne transmission - vibration - gym - gyms - fitness - sport facilities - sports facilities - noise control of gyms - activity noise break out - noise breaking out - amplified music noise - noise transfer through the internal building fabric of sport , gym and fitness facilities - plasterboard - drylining - dense plasterboard lining - increase the size of the cavity acoustics - acoustic design - airborne transmission - vibration - gym - gyms - fitness - sport facilities - sports facilities - noise control of gyms - activity noise break out - noise breaking out - amplified music noise - noise transfer through the internal building fabric of sport , gym and fitness facilities - plasterboard - drylining - dense plasterboard lining - increase the size of the cavity
  • some decoupling elements to increase their performance such as
    • acoustic studs
    • resilient clips
    • resilient bars
    • or even make the studs independant from the outer structure.

Note: If the facility is to move in an existing building, sound insulation testing are necessary to rate the performance of the separations elements and work out the best solution for improvement.

Note: sometimes, a full box-in-box construction will be necessary

 

Noise transfer via the ventilation systems 

of sport, fitness and gym facilities

What happens?


The music and activity noises from sport, fitness and gym facilities:

 

  • ‘enter’ the ventilation systems
  • propagate through the ducts, and;
  • break outside or in another space within the same building (although this last one is unlikely because most facilities have their dedicated ventilation system).

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What are the noise control solutions?


To control the noise transfer via a ventilation system, you can think about the following solutions. 

Solution 1:

Install attenuators

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This is probably the most common and easiest solution.

Their performance mainly depends on their length and their free area.

However, be aware that attenuators shouldn’t be installed anywhere in the ductwork for optimal acoustic performance.

The best locations to install the attenuators are:

 

  • centered in the wall separating the noisy space and the rest of the building;

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  • or at the wall separating the noisy space and the rest of the building.  

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Solution 2:

Strategically locate the inlets and outlets

 

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Ideally, you should locate the inlets and oulets of a ventilation system as far away from the sensitive receptors as possible. (although some sites/buildings don’t offer a great amount of flexibility).

This way, you can reduce the performance of the attenuators (and save some cost)… or completely omit them

 

 

Solution 3:

Select larger and square ducts (for low frequency attenuation)

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If you need to attenuate low frequency sounds, you could think about selecting large and square ducts. 

 

Note:  This is only worth if:

  • you have long runs of ductwork.

  • you have enough space for large ducts.

 

 

Solution 4

Select lined ducts

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Lined ducts attenuate more noise than unlined ducts.

Therefore, you can use them to attenuate some amount of music and activity noise. 

 

Note: it is only worth if:

  • you have long runs of ductwork.
  • the pressure drop they create doesn’t require a higher air flow (which would be counter productive). This needs to be checked with the mechanical engineer on board. 

 

 

Control of sound reverberated (i.e. reflected)

in sport, fitness and gym spaces

What happens?


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Within most sport, fitness and gym spaces, medium to high levels of sound are generated.

With a majority of hard surfaces (i.e. sound reflecting), the spaces can be very reverberant and amplify these sounds.

This also makes it harder to control the noise transfer from the gym to other receptors (within or outside of the same building).

What is the noise control solution?


To reduce that reverberation effect, you need to include sound absorptive finishes on the walls and the ceiling.

Where possible, it is useful to install a carpet to contribute to the sound absorption

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Noise and vibration challenges in sport, fitness and gym facilities Part 1: Site Analysis - acoustic consultant - noise control - gym acoustics - vibration control - gym vibration

Noise and vibration challenges in sport, fitness and gym facilities

Part 1: Site Analysis


In sport, fitness and gym facilities, you find a lot of activities and equipment that create noise and vibrations.

If not controlled correctly, they can disburb neighbouring sites, neighbouring premises, and even the facility itself.

Atelier Crescendo have created this series of posts to make you understand:

 

  • which activities are disturbing.
  • how they are disturbing.
  • who / what they can be disturing to.
  • what the solutions are to reduce the noise and vibration disturbance. 

 

This post suggests the first step of such a process: a complete and thorough Site Analysis.

Site analysis of sport, fitness and gym facilities

 

A complete and thorough site analysis of a facility serves the design of efficient and cost effective acoustic solutions.

Therefore, this first post lists a few questions to ask yourself for a site analysis and explains why they are important

 

 

(click on each link to access the relevant section)

 

 

What are the activities proposed?

 

Various activities and equipment in sport, fitness and gym facilities produce noise and/or vibrations.

They do it in very different ways and at different intensities, leading to require very specific control solutions.

This section gives you a few examples of such activities and equipment.


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Loud amplified sound

Most fitness and gym facilities play background music which is generally not a problem.

However, loud music (or sounds) may be played in some areas such as:

  • activity and dance studios
  • sports halls during events
  • external sport areas during events
  • others

Therefore, knowing which areas will produce loud amplified sound is important to take into account in the site analysis.

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Vibrating machines

Some equipment that including rotating system (of some sort) not only produce noise but also vibrations. This includes:

  • treadmills
  • bikes
  • ellipticals
  • others

The above equipment produces (relatively) mild but ‘constant’ vibrations that are transmitted to the building structure.

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Resistance machines

Most resistance machines involve lifting a stack of weights indirectly by performing a specific movement. They include:

  • chest press
  • leg press
  • lat pulldown
  • cable biceps/triceps bar
  • seated row
  • shoulder press
  • others

Each time the stack drops, it creates an impact. This impact produces vibrations that are then transmitted to the building structure.

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Functional training and sport areas

Sport, fitness and gym facilities sometimes include functional training and/or sport areas

All these activities involve medium (up to 20-30 kg) or body weights dropped from heights that usually don’t exceed knee height (i.e. about 0.5 m).

They create repeated and (sometimes) synchronised impacts that produce vibrations of ‘medium intensity’.   

They include: 

  • running tracks
  • slam ball/wall ball work
  • sports pitches
  • sports courts (tennis)
  • sled training
  • TRX training
  • kettlebell training
  • others

Free weight areas - barbell - Noise and vibration challenges in sport, fitness and gym facilities Part 1: Site Analysis - acoustic consultant - noise control - gym acoustics - vibration control - gym vibration

Free weight areas

Free weight areas are probably the most challenging areas to isolate in sport, fitness and gym facilities. 

Most of the time, they involve:

  • using medium (up to 20-30 kg) to very heavy (more than 50 kg) weights. 
  • lifting them from knee to above head height.
  • Dropping them on the floor in, most of the time, an uncontrolled manner.

This process creates a very strong impact, with a lot of energy transmitted, that can be very difficult to mitigate

 

Who could the facility disturb? 

(i.e. what are the noise sensitive receptors)

What is a noise sensitive receptor

 

It is a property or a space located within the same building as the gym/sport facility or close to the site.

Examples of such receptors could be:

 

  • Residential properties
  • Commercial properties (i.e. offices, retail, etc)
  • Education facilities
  • Facilities with equipment sensitive to vibrations (such as laboratories, precision engineering facilities, etc)

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One of the reasons why a site analysis is important is to help set relevant target for the acoustic treatment(s) should achieve.  

This target, or also criterion, highly depends on the who/what the facility is likely to disturb

Some noise sensitive receptors are more sensitive than others (see beside what a noise sensitive receptor is). For example:

 

  • dwellings are generally more sensitive to gym noise  than commercial properties (especially at night).
  • Offices are more sensitive than retail premises
  • Some laboratories may have equipment sensitive to levels of vibrations that are not perceptible by the human body.

 

For residential receptors, you usually discuss and agree with the Local Authority. For other receptors, you could agree a criteria with the landlord or the neighbouring facilities.

Therefore, understanding who your sport, fitness and gym facility might disturb will help define the level of noise and/vibration mitigations

 

Where are the noise sensitive receptors? 

Will they be disturbed by airborne noise, structure-borne noise or both? 

 

Knowing where the noise sensitive receptors are allows you to know if the cause of the disturbance is:

Just airborne noise

Note: What is airborne noise? it is noise that only propagates through the air or the atmosphere. 

 

It is the case when the facilities and the receptors are structurally disconnected (i.e. not part of the same building).

 

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Airborne noise of sport, fitness and gym facilities

 

Just  ‘structure-borne’ noise

Note: What is ‘structure-borne’ noise? it is noise generated by vibrations that propagate through a structure (mostly building structures here) and are re-radiated into noise.

 

It is the case when the facilities and the receptors are structurally connected (i.e. they are part of the same building) but are fairly remote from one another (i.e. not adjacent) 

 

Structure-borne noise - structure borne noise - Noise and vibration challenges in sport, fitness and gym facilities Part 1: Site Analysis - acoustic consultant - noise control - gym acoustics - vibration control - gym vibration
Structure-borne noise of sport, fitness and gym facilities

 

Or both airborne noise and ‘structure-borne’ noise (and maybe pure vibration as well):

It is the case when the facility and the receptors are structurally connected and are close to one another (or even adjacent!). 

 

airborne noise - Structure-borne noise - structure borne noise - Noise and vibration challenges in sport, fitness and gym facilities Part 1: Site Analysis - acoustic consultant - noise control - gym acoustics - vibration control - gym vibration
Structure-borne and airborne noise of sport, fitness and gym facilities

 

 

The relevant acoustic treatment to control the noise and/or vibrations from the facility varies for each situation above.

 

 

When will the facility operate? 

Knowing when (i.e. which periods of the day) a sport, fitness and gym facility will operate

is very important to set relevant noise and/vibration control criteria

Choosing to operate a facility, with loud music and/or heavy impacts on the floor, during late evening and night time periods is likely to increase the cost of acoustic treatment needed.

Especially, when the facility is near or adjacent to dwellings

 

Note: Late evening is approximately after 19:00 hours. Night time is approximately between 23:00 and 07:00 hours.

 

The reason of this is because you need to set very strigent noise/vibration criteria for the activities to not cause any disturbance to neighbours needing to rest or sleep

External noise levels are also lower between 19:00 and 07:00 hours, so the activities or the music are more audible to neighbours.

 

Note: This section might be redundant as a lot of sport, fitness and gym facilities operate 24/7 and their peak hours are generally early in the morning (between 06:00 and 08:00 hours) and in the evening (between 17:00 and 20:00 hours)

 

operating hours - gym operation - Noise and vibration challenges in sport, fitness and gym facilities Part 1: Site Analysis - acoustic consultant - noise control - gym acoustics - vibration control - gym vibration

 

What is the structure of the building where the facility is? 

 The structure of a building has a big influence in the acoustic treatment required.

Structure impact - Noise and vibration challenges in sport, fitness and gym facilities Part 1: Site Analysis - acoustic consultant - noise control - gym acoustics - vibration control - gym vibration

 

The structure of the building influences: 

 

  • The sound insulation treatment for the floors and the walls.
  • The vibration isolation treatment for the floors.

And you will generally need less material for heavy and stiff structures than for light structure. 

Examples of heavy structures are in-situ concrete structures, brickwork, etc.

Examples of light structures are timber, mass timber, pre-cast concrete and metal frame structures.

 

Note: If you want to install a free weight area on a timber structure, it will be very challenging, or expensive, to control the ‘structure-borne‘ noise generated by the impacts of the weights on the floor.

(see above Section Where are the noise sensitive receptors?  above for the definition of ‘structure-borne‘ noise) 

 

 

 

 

What is the layout of the facility? 

 (i.e. where will the different activities go)

Planning the facilities layout is an integral part of noise and vibration control strategy.

It may be obvious, but:

the further you locate the noisy and vibrating activities from the sensitive receptors,

the less materials and acoustic treatment you need.

So by just optimising the layout of a facility, you can already control the noise and vibration impacts of the activities.

Below are three types of areas that are worth considering for such as process.

Note: The last two points are particularly useful to know if you need to select different sites and assess their suitability for  sport, fitness and gym use.

football pitch - hockey pitch - external sport areas - sport pitches- running track - Noise and vibration challenges in sport, fitness and gym facilities Part 1: Site Analysis - acoustic consultant - noise control - gym acoustics - vibration control - gym vibration

External running tracks, sport pitches and other  areas

Some external sport areas produce noise that can be particularly disturbing when they are close to sensitive receptors. 

Therefore, by locating these areas strategically, you can avoid some solutions like acoustic fences or earth bunds.

There are two main strategies here. Either you locate the areas:

  • away from the receptors, or;
  • ‘behind’ the some buildings (that of the facilities for example) that you use as acoustic screens.

Obviously, they are very much site dependant and sometimes can’t be implemented

 

studios - dance studio - sports hall indoor areas - sports halls - Noise and vibration challenges in sport, fitness and gym facilities Part 1: Site Analysis - acoustic consultant - noise control - gym acoustics - vibration control - gym vibration

Studios, sports halls and other indoor areas

Most studios, sports hall and other indoor areas organise noisy activities or events with loud amplified sounds.

They can be particularly disturbing to receptors within the same building or in a neighbouring building

Although you can control noise (and vibrations!) from these areas with the finishes and the construction of the building. It is also worth thinking about locating them as far away as possible from the receptors … when possible. 

Another solution is to use secondary spaces (like bathrooms, stores, locker rooms, etc) as ‘buffer’ areas between the noisy spaces and the receptors. 

free weight areas - barbell - kettlebell - treadmill - elliptical - gym bike - Vibrating machines - Noise and vibration challenges in sport, fitness and gym facilities Part 1: Site Analysis - acoustic consultant - noise control - gym acoustics - vibration control - gym vibration

‘Vibrant’ equipment and activities

 

The vibrations generated by some equipment and activities (such as  free weight activities, skate parks and even sports courts and studios) can be particuarly complicated and/or expensive to control.

Therefore, it will always be useful to think where they can go in the facilities to minimise the amounts of anti-vibration materials

  • at ground floor level and/or on heavy slabs.
  • As far away as possible from the sensitive receptors.

 

 

Suspended acoustic rafts explained

 

Have you ever wondered what suspended acoustic rafts are and how they acoustically work?

This page briefly explains:

  • what suspended acoustic rafts are exactly
  • which sound absorption performances acoustic rafts achieve and, most importantly, how they should be specified
  • which materials are usually used for acoustic rafts
  • examples of acoustics rafts products available on the market
 

 

Are you looking to understand how acoustic products work and find examples available on the market? 

Visit the Acoustic Design Catalogue by clicking on the button below.

 

What are suspended acoustic rafts?

Suspended acoustic rafts are free-hanging and flat elements made with a thick fibrous or porous materials that have sound absorption qualities. You hang them horizontally at a certain distance from a hard surface (usually a soffit).

They are a popular option to reduce the sound reverberation in:

  • education spaces
  • office spaces
  • assembly spaces
  • public spaces (such as receptions, entrance halls, etc)

 

Brief description of suspended acoustic raft systems

Suspended acoustic rafts - sound absorption - acoustic absorption - acoustic consultant - acoustic design - architectural acoustic design

Although acoustic rafts are mostly square or rectangular, some of them are also roundoval or any other bespoke shape.

Some raft manufacturers/suppliers give the option to include lighting and other electrical systems within the rafts.

 

Sound absorption performance of suspended acoustic rafts

The sound absorptive materials used for suspended acoustic rafts generally achieve sound absorption Class AClass B or Class C.

However, you should know that sound absorption classes are generally for a materials fixed to a hard surface with only one side visible. This side is the only one that absorbs sound. The other one doesn’t.

For acoustic rafts, it is a little bit different.

 

Suspended acoustic rafts – Sound absorption below and above

Not only the underside of the rafts absorbs sound, but also upper side indirectly.

Sound will first hit the hard surface above the acoustic rafts and then the upper side of the rafts.

Therefore, the distance between the rafts and the hard surface above has an influence on the sound absorption of the raft systems. Below approximately 1m, the further the rafts from the hard surface, the higher the sound absorption at mid and high frequencies.

 

Sound absorption below and above the rafts

sound absorption below and above the rafts - Suspended acoustic rafts - sound absorption - acoustic absorption - acoustic consultant - acoustic design - architectural acoustic design

Suspended acoustic rafts – Sound absorption of the edges

The edges of the rafts also absorb sound.

So a couple of large acoustic rafts absorb a little bit less sound than a few smaller acoustic rafts (with the same amount of absorptive materials).

 

Sound absorption of raft edges

sound absorptive edges - Suspended acoustic rafts - sound absorption - acoustic absorption - acoustic consultant - acoustic design - architectural acoustic design

Suspended acoustic rafts – Examples of sound absorption performances

To illustrate this, the graphs below shows examples of sound absorption performance for various raft systems.

 

Note: for rafts, the sound absorption performance is qualified in terms of equivalent absorption area per unit. Not in terms of sound absorption coefficient per m² of material.

 

Equivalent absorption area (m²) of 1200mm x 1200mm acoustic rafts located at different distances from the hard surface above 200 mm, 400 mm and 1000 mm and spaced 500 mm apart (Courtesy of Ecophon)

Equivalent absorption area (m²) of 1200mm x 1200mm acoustic rafts located at different distances from the hard surface above 200 mm, 400 mm and 1000 mm and spaced 500 mm apart (Courtesy of Ecophon) - sound absorptive edges - Suspended acoustic rafts - sound absorption - acoustic absorption - acoustic consultant - acoustic design - architectural acoustic design

 
 
Sound absorption per m² of raft based on rafts of different sizes hung at 1000mm from the hard surface above
(Courtesy of Ecophon)

Sound absorption per m² of raft based on rafts of different sizes hung at 1000mm from the hard surface above (Courtesy of Ecophon) - sound absorptive edges - Suspended acoustic rafts - sound absorption - acoustic absorption - acoustic consultant - acoustic design - architectural acoustic design

Suspended acoustic rafts – Specification

Based on the above, you can now understand that the sound absorption characteristics of raft systems don’t just depend on the material of the rafts.

Therefore, in the acoustic specifications, it is important to include the following information:

  • the sound absorption of the material installed in a room (when measured in line with ISO 354:2003 Acoustics — Measurement of sound absorption in a reverberation room)
  • the size of the rafts
  • the spacing between the rafts
  • the distance between the rafts and the hard surface above.

 

Note: the above is applicable to any other free hanging suspended acoustic system.

 

Materials used for suspended acoustic rafts

The materials preferred for acoustic rafts are usually thick fibrous or porous sound absorptive materials such as:

  • fibre glass
  • mineral wool
  • wood wool and mineral wool on top
  • polyester fibres
  • wood fibres

Sometimes, the sound absorptive material is wrapped in a fibrous fabric or even painted.

 

Examples of suspended acoustic rafts

To find examples of suspended acoustic raft products, visit the Acoustic Design Catalogue here.

 

Acoustic plaster systems explained

Have you ever wondered what acoustic plaster systems are?

This post explains:

  • What are acoustic plaster sytems?
  • Advantages and uses of acoustic plaster systems
  • Configurations and characteristics of acoustic plaster systems
  • Sound absorption / acoustic absorption of acoustic plaster systems
  • Sustainability of acoustic plaster systems
  • Installation and workmanship for acoustic plaster systems
  • Examples of acoustic plaster products available on the market

 

Note: Although acoustic plaster systems do look really good, they might not be the solution if you are on a tight budget. Some of the reasons are because they include some high-end materials and have to be installed by specialists.

 

 

What are acoustic plaster systems?

Acoustic plaster systems are sound absorbing systems that are made of fibrous and porous materials to help reduce sound reverberation within spaces.

 

Advantages and uses of acoustic plaster systems

Acoustic plaster systems are usually installed on the ceilings, the soffits and sometimes the walls.

Their advantages are:

  • they have a seamless and smooth appearance.
  • they can be curved or shaped to follow a custom design.
  • they can sometimes integrate heating and cooling systems.
  • although white is preferred most of the time, they can be tinted or painted (with approved paint) in different colors.

Acoustic plasters are generally fire-resistant and can be made moisture resistant.

Lighting systems, sprinklers and audio systems can also be integrated.

Slide the images in the gallery below to see what acoustic pasters look like. To find examples of acoustic plaster products, visit the Acoustic Design Catalogue here.

 

Configurations and characteristics of acoustic plaster systems

Acoustic plaster systems usually come in pre-made panels that require final finishing on site.

They usually include the following:

  • a thick sound absorptive backing layer made of mineral wool, glass fibre, natural fibre or foam.
  • a porous (acoustically transparent) and more rigid base layer.
  • a thin finish layer of plaster trowel or spray applied to the backing layer.
  • a second thin layer can be applied to provide a finer finish.

The thickness of the panels ranges from approximately 10mm to 70 mm.

They can either be fixed to a hard surface or as part of a suspended ceiling (in which case, the thickness of the whole system can reach approximately 220 mm).

Acoustic plaster configuration - suspended ceiling - backing sound absorptive layer - base layer - plaster finish layer - second plaster finish layer - hard surface
Acoustic plaster configuration

 

 

Sound absorption / acoustic absorption of acoustic plaster systems

The sound absorption performance of acoustic plasters depends on:

  • the material of the backing layer.
  • the thickness of the backing layer.
  • the porosity of the surface finishes.
  • if fixed to a suspended ceiling, the depth of the ceiling cavity.

The sound absorption characteristics of acoustic plasters are considered for each square meter of material and can achieve a large variety of performances ranging from Class D to Class A

 

Note: The sound absorption characteristics of acoustic plasters increase with the thickness of the panels, the size of the cavity behind the panels and the presence of a backing layer behind the panels.

 

As mentioned above, plasters can also be painted provided the paint is approved by the manufacturer. This is because paint can modify the porosity of the finish layer and change the sound absorption capacity of the system.

 

Sustainability of acoustic plaster systems

Some plaster systems use natural or recycled materials (such as recycled glass granulate) for the backing layer.

The plaster finish can be made from cellulose, glass or marble granular aggregate, which is a secondary material obtained from the production of natural stone.

 

Installation and workmanship for acoustic plaster systems

Installing acoustic plaster systems requires a high level of workmanship to obtain the sound absorption performance desired and avoid cracks appearing with time.

Suppliers either have in-house and trained installers or certified installers.

 

Examples of acoustic plaster products

To find examples of suitable acoustic plaster products, visit the Acoustic Design Catalogue here.

 

music rehearsal hall - music rehearsal room - orchestra - natural light - acoustics - public performance - acoustic - acoustic consulting - acoustic consultant - performing arts - theatre consulting - acoustic design - architectural acoustic design

 

Design of music rehearsal rooms – Part 3: Other general considerations for rehearsal rooms

Part 1 was going through the aspects that would make successful the acoustic design of music rehearsal rooms.

Part 2 dived deeper into acoustic design with some tips for the planning of such spaces.

Part 3 here goes through other general considerations for rehearsal rooms, including:

  • answering the needs of the main performance space (within large facilities)
  • facilitating access to new audiences
  • providing comfort for the musicians
  • turning rehearsal rooms into performance spaces
  • access and practicalities

It was written by Duck Sceno (Theatre Consultants) with some contributions from Atelier Crescendo. 

Answering the needs of the main performance space

Each type of performance venue has specific needs for the rehearsals.

  • Theatres and Opera houses need a room close to the dimensions of the main stage, with the possibility of installing pieces of set and creating similar light and sound.
  • As well as requiring piano rooms for soloists, Opera houses also need large rooms for choirs and orchestra.
  • Concert halls and Philharmonies need an (or multiple) orchestral rehearsal room(s) able to accommodate a symphony orchestra with optimal acoustic conditions.

Atelier Crescendo’s comment: If the rehearsal room is part of a larger facility, it might be wise to locate it away from other sensitive and/or noisy areas (such as other rehearsal rooms, performance spaces, recording rooms, music practice rooms, etc). This way, you minimise the acoustic interferences between the spaces when they are used simultaneously

 

Rehearsal halls and control room

 

 

Of all the performances, opera and symphonic music are those that remain the most traditional because they are linked to a majority of old musical works, with an audience made of specialist who does not always want to make this art accessible.

Operas can be more accessible because they follow the codes of theatres, that are more democratised, with the spectators facing the stage. People can be more or less seduced by the show. However, they can listen to the music, see the acting and can even sleep (!!) because no one is looking in their direction.

Symphonic music is in itself more difficult to access. The orchestra is the only visual show. There are no sets, no costumes, and the audience surrounds the performers. This allows anyone to watch the yawning and sleepy novices and any other attitudes that would not be appropriate.

 

The rehearsal room can facilitate access to new audiences

High urban densities of large cities have forced the construction of new performance venues outside of the city centres and far from their historical audience.

Between the venue and its adopted neighborhood, the rehearsal rooms are becoming places to gather and exchange where local amateur orchestras and younger musicians can play.

It is also an opportunity to open the building to a new audience and create links with it .

The rehearsal rooms should therefore be made very accessible on the ground floor at lobby level.

 

Providing comfort to the musicians

Transparent, windows and/or glazed façades bring natural light and therefore extra comfort to the professional musicians for whom the rehearsal rooms are actual working places. They also allow the public to see what happens inside.

music rehearsal hall - music rehearsal room - orchestra - natural light - acoustics - public performance - acoustic - acoustic consulting - acoustic consultant - performing arts - theatre consulting - acoustic design - architectural acoustic design
Rehearsal hall – Provision of natural light

When professional musicians are not rehearsing, these rooms can turn into incubators for young future talents who will come to practice together.

 

Turning rehearsal rooms into performance spaces

Rehearsal rooms must be able to transform into small / informal performance spaces.

Rehearsal hall – Piano and small orchestra

Rehearsal hall – Public performance and grand orchestra

 

They need to be able accommodate unexperienced audiences installed in a frontal configuration, with a clear separation between the stage and the audience, to focus more on music and its feelings.

Concequently, the rooms need to achieve scenographic, acoustic and safety requirements. It will be necessary to design and study the installation and the sightline of the audience, the concealment and the control of the natural light with curtains and lightlock accesses.

Atelier Crescendo’s comment: the acoustic contribution of the seats will also need to be considered. 

Rehearsal hall – Provision of retractable seating

 

 

A control room, part of the technical infrastructures, might be useful with open access to promote creativity and inspire future performances.

The acoustics will have to be variable according to the use of the room (it is for a rehearsal or a show? with or without an audience? with a small or a large orchestra? with amplified or purely acoustic music?).

Atelier Crescendo’s comment: This can be done with “passive” variable acoustic systems. Read Variable sound absorption systems for more information. It is also possible to use “active” variable acoustic systems with electro-acoustic systems (using microphones, loudspeakers and special audio processing devices).

Rehearsal hall – Control room

 

Access and practicalities

Like any space open to the public, it will be necessary to study the number and the dimensions of the accesses and the circulations.

The installation conditions for the public with emergency lighting and signage, and taking into account all the publics including people with reduced mobility.

 

The function of the rehearsal rooms is important. Their technical aspect is even greater as their “small” size requires optimisations. Their need for a high flexibility requires specific studies and mixed infrastructures. Rehearsal rooms are not always considered at their fair value in briefs / programs and budgets, in France and on international projects.

 

 

Design of music rehearsal rooms – Part 2: Some acoustic design tips for music rehearsal rooms

Part 1 was explaining what makes a successful acoustic design for music rehearsal rooms.

Part 2 here dives deeper into acoustic design by giving you a few tips for the planning of such spaces. It covers the following topics:

At the end of this part, you will also find all the documents and the materials reviewed to help writing the articles. 

Part 3, written by Ducks Sceno (Theatre Consultants) with contributions from Atelier Crescendo, highlights other general design considerations you should think about for rehearsal rooms.

Enjoy the read.

 

Sound reverberation conditions for music rehearsal rooms

Good sound reverberation conditions in a large music rehearsal rooms contribute to: 

  • the audibility and the clarity of the musical messages
  • the musical intonations
  • the musical tones 
  • the articulations
  • the balance of the sounds

Therefore, unsurprisingly, getting the reverberation conditions right is THE focus point for the acoustic design.

You need to consider:

  • the overall sound reverberation quality of the rehearsal room to control the loudness and the clarity of the music played. You usually do this by adjusting the volume and the general amount of sound absorptive/reflective materials.

 

Note: read Sound reverberation – Part 1: Basics if you need a refresher about sound reverberation and reverberation time. 

 

  • the timing of the sound reflected back to the musicians (Do you remember? Part 1: The goals for a successful acoustic design explains the necessity to balance early and late reflected sound for musicians on stage). You manage this by adjusting the orientation and/or the shapes of the surfaces around the musicians and the orchestra conductor. Sometimes, you also need to add surfaces such as overhead reflectors, orchestra shells, etc. 

 

reflected sound energy - sound reflections -- stage acoustics - direct sound - early reverberation - late reverberation - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

  • the frequency content of the sound reflected back to the musicians (Do you remember? the end of Part 1: The goals for a successful acoustic design explains that musicians like to hear rythms and musical expressions that are mostly emitted at medium and high frequencies). Therefore, the reflected sound should contain less energy at low frequencies than at higher frequencies. You manage this by adjusting the dimensions and physical properties of the finishes and the materials (ex: thickness, width, length, density or also stiffness) around the musicians, so that they absorb more energy at low frequencies. 

reflected sound energy around the musicians - low frequencies - - stage acoustics - medium 'mid' frequencies - hiigh frequencies - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

 

 

Volume and space for music rehearsal rooms

Part 1: The goals for a successful acoustic design explains that containing the sound energy of the music is key to ensure a successful rehearsal room.

For large ensembles (including 20 musicians), the room volume should to be relatively large so that the music doesn’t sound too loud. If the ensembles include loud instruments (such as brass instruments or also percussions), the volume should be even larger

You shoud also set an area where artists will sit (or stand!) and make sure they are not too close to (vertical and flat) acoustically reflective surfaces like the walls. 

Norwegian Standard 8178:2014  – Acoustic criteria for rooms and spaces for music rehearsal and performance  provides guidance on the necessary volume and space  for music rehearsal and perforance spaces depending on the type of music played inside. Read Acoustic design planning for music spaces  for more details. 

 

Note: The international standard ISO 23591:2021 – Acoustic quality criteria for music rehearsal rooms and spaces provides the same guidance.

 

For large music ensemble rooms with more than 20-25 musicians (our case here), you should consider the dimensions below.

Volume and space - stage acoustics -- ISO 23591:2021 - Acoustic quality criteria for music rehearsal rooms and spaces - Norwegian Standard 8178:2014  - Acoustic criteria for rooms and spaces for music rehearsal and performance - room height - net volume - net area - performers - room proportions and geometry - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

QUIET MUSIC

(just string instruments, choirs, etc)

 

Net volume

minimum 700 m3

 

 

 

 

Net floor area

minimum 50 m2

+

minimum 2 m2 /musician

 

Soffit / Ceiling height

minimum 5 m

LOUD MUSIC

(i.e. brass bands, concert bands, big bands,

percussion ensembles, symphony orchestras)

Net volume

minimum 30 m3 / musician

concert bands: minimum 1000 m3

brass bands: minimum 1500 m3

Symphony orchestras: minimum 1800 m3

 

Net floor area

minimum 120 m2

+

minimum 2 m2 /musician

 

Soffit / Ceiling height

minimum 5 m

 

 

Room proportions and geometry for music rehearsal rooms

One of the most successful shapes for large music ensemble rooms is the cuboïd shape such as a cube or the so called ‘shoebox’ shape. 

  What is a room with a shoebox shape? It is a room with a rectangular floor area, parallel side walls and tall ceiling / soffit. The base volume is two cubes located next to one another.

Room proportions and geometry - shoebox shape - cube - squares - stage acoustics -- acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

However, sound diffusive finishes and/or shapes should be planned to avoid creating flutter echoes.

You should also avoid any shapes that focus the sound in certain areas. This is because the sound field should be as ‘diffuse’ as possible in the room.

 

Note: you obtain a diffuse sound field in a space when the sound pressure level is uniform throughout the space. 

 

Examples of shapes that focus sound are presented below.

avoid

Concave shapes

 

Dome

Dome - concave shapes - shapes to avoid - Room proportions and geometry -- stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

Curved wall 

curved wall - shapes to avoid - Room proportions and geometry - stage acoustics -- acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

Avoid

pitched/slanted Shapes

 

Pitched ceiling

- stage acoustics -slanted roof - slanted ceiling - slanted soffit - pitched roof - pitched ceiling - pitched soffit - shapes to avoid - Room proportions and geometry - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

Angled walls

angled walls - shapes to avoid - Room proportions and geometry -- stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

 

Acoustic treatment for music rehearsal rooms

For large music rehearsal rooms, it is very likely that most walls need to include some acoustic treatment (or at least acoustic consideration) in the form of sound absorption or sound diffusion.

The function of the acoustic treatment varies depending on:

  • the location of the walls in relation to the orchestra
  • the height of the wall section considered.

Therefore, this section presents acoustic design tips for :

  • the wall behind the conductor
  • the walls at low level
  • the walls at upper level

Acoustic treatment for the walls of music rehearsal rooms

Wall behind the orchestra conductor

The wall behind the orchestra conductor should include some amount of sound absorption and/or diffusion.

This avoids strong ‘specular’ reflections to hit the wall and reach the conductor again, creating the perception of a virtual orchestra behind her/him (see below, specular and diffusive reflections are explained).

flat and solid wall acoustically reflective behind the conductor - virtual orchestra perceptible - stage acoustics -- acoustic treatment for the walls - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

acoustically absorptive wall behind the conductor -- stage acoustics - virtual orchestra less perceptible or imperceptible - acoustic treatment for the walls - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

irregular wall acoustically diffusive behind the conductor - - stage acoustics - virtual orchestra less perceptible or imperceptible - acoustic treatment for the walls - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

Note: what is a specular reflection? a specular reflection is, similarly to light reflected on a mirror, a reflection that bounces off a surface with the same angle as when it hits the surface. A diffusive reflection is a reflection that bounces off a surface in different directions

 

 

angle of incidence - angle of reflection - incident wave - stage acoustics -- reflected wave - specular reflection - diffusive reflection - virtual orchestra less perceptible or imperceptible - acoustic treatment for the walls - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

Walls at low level

Assuming most musicians face the conductor, you should avoid sound absorbing finishes at low level, i.e. approximately below head height. Instead, you should favor elements that reflect and diffuse sound at medium and high frequencies

This ensures that the conductor and the orchestra receive lateral sound reflections (musicians rely more on lateral reflections to hear themselves and others).

sound diffusive lower side walls - lower walls - acoustic treatment for the walls - - stage acoustics -acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

However, there could be an option for these surfaces to absorb some amount of acoustic energy at low frequencies.

For this applications, materials that can absorb sound at low frequencies generally include:

  • a sheet / board /face that is not so dense 
  • a cavity behind with sound absorption inside as an option.

Examples of such materials are:

  • plasterboard or gypsum based boards on frame
  • timber sheets/boards mounted on frame
  • suspended ceilings

 

Note: There are many other specialist materials and configurations that can absorb sound at low frequencies.

 

On the walls located far from the musicians, it might be necessary to install sound absorbing finishes to avoid any late (or unwanted) reflected sound.

 

Walls at upper level

The upper walls, i.e. approximately above head height, can include sound diffusive surfaces.

However, they are a good location to add broadband absorption materials to lower the overall sound reverberation within the rehearsal room.

 

What are broadband absorption materials? they are materials that absorb sound over a large range of frequencies. Examples of such materials are fibre, wool or also foam based materials.  

 

sound diffusive upper side walls - sound absorptive upper side walls - upper walls - - stage acoustics - acoustic treatment for the walls - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

Acoustic treatment for the ceiling / soffit of music rehearsal rooms

A fully or partially sound absorptive ceiling can also be useful to reduce the overall sound reverberation within the rehearsal room. Especially when you need to absorb sound at low frequencies

 sound absorptive ceiling with cavity (optional) - acoustic treatment for the ceiling soffit - - stage acoustics -acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

Acoustic consideration for the floor of music rehearsal rooms

Hard floor finish fixed on concrete hardly absorbs any sound. 

However, a raised hard floor finish can absorb sound at some low frequencies due to the cavity created by the system.

This feature can be particularly useful for the musicians who rely on reflected sound at medium and high frequencies (as mentionned previously). 

For the same reason, carpet should be avoided as it absorbs sound at medium and high frequencies.

See below some ideas of sound absorption performances achieved by different floor finishes. 

 

Sound absorption coefficients of different floor finishes
(ref: Acoustic Absorbers and Diffusers, Theory, Design and Application – Third Edition – Trevor J. Cox and Peter D’Antonio)

 

 

 

 

Overhead reflectors for music rehearsal rooms

For large and tall spaces where large orchestras play, it might be necessary to plan for sound reflectors above the musicians, also called ‘overhead reflectors’

They are useful to provide additional early reflections and improve the acoustic conditions within the orchestra. Sometimes, additional wall reflectors above head height or even orchestra shells are also installed to provide the same effect.

For large (and loud) ensembles, overhear reflectors should be at approximately 8-10 m above the floor level.

For small (and quiet) ensembles, they could be located as low as 6 m above the floor level . 

 

If the overhead reflectors are too low, they could cause some loudness issues (i.e. the music will sound too loud)

 

You should favor arrays of smaller reflectors, instead of a single large reflector or just a few large reflectors, to optimise the diffusion of the acoustic energy across the orchestra. 

Some of the most common shapes for overhead reflectors are curved (convex), random waves, ‘QRD’ type (‘QRD’ stands for Quadratic Residue Diffuser) or any other shapes with irregular and random width and depth.

Flat reflectors should also be avoided.

See below some examples of acoustic diffusers (although many other types of diffusers exist). 

single reflector - single curved reflector - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

array of reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

array of profiled reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

 curved reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

round mushroom reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

3D QRD diffusers - 3D QRD reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 random wave diffusers - random wave reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

You should favour relatively dense and stiff materials to ensure that sound hitting the reflector is not absorbed, especially at the lower frequencies due to the resonance of the reflectors.

Examples of materials are:

  • gypsum based
  • dense plaster
  • wood particle or fibre based
  • glass

Did you know? even with a dense and stiff material, a flat reflector can resonate and absorb sound at low frequencies. Curving it will stiffen it, increase its natural frequency and reduce the low frequency absorption. 

 

 

 

Background noise levels in music rehearsal rooms

A music rehearsal room is an environment where the musicians need to hear their own musical details and those of the other musicians. 

Because a high background noise can mask these details, it is important to keep it as low as possible when the space is in use. 

Sometimes, music rehearsal rooms are also used as large recording studios for large ensembles and orchestras. So it is important to ensure acoustic conditions suitable for recording activites, i.e. with a very low background noise levels.

Therefore, the acoustic design should include control of noise from (some of or all) the following sources:

  • ventilation systems
  • mechanical systems and machineries
  • electrical systems
  • external noise (such as road, air or even rail traffic)

 

References for acoustic design of music rehearsal rooms

The following documents and materials have been reviewed to write this article and Part 1: The goals for a successful acoustic design .

  • J. Meyer – Some problems of opera house acoustics – Proceedings – Symposium on acoustics and theatre planning for the performing arts (1986)
  • P. Adams – Acoustic design of large rehearsal spaces – Proceedings – ISRA (2019)
  • A. Gade – Investigation of musicians’ room acoustic conditions in concert halls, Part I: Field experiments and synthesis of results – Acustica (1989)
  • A. Gade – Investigation of musicians’ room acoustic conditions in concert halls, Part II: Methods and laboratory experiments – Act Acustica United & Acustica (1989)
  • International Standard Organisation – “ISO 3382-1 – acoustics measurement of room acoustic parameters – Part 1: Performance spaces” (2009)
  • R. Wenmaekers – How orchestra members influence stage acoustic parameters on five different concert hall stages and orchestra pits – Journal of the Acoustical Society of America ‘JASA’ (2016)
  • J Dammerud – Attenuation of direct sound and the contributions of early reflections within symphony orchestras – ournal of the Acoustical Society of America ‘JASA’ (2010)
  • L. Panton – Investigating auditorium acoustics from the perspective of musicians – PhD  thesis – University of Tasmania (2017)
  • European Parliament and Council, Directive 2003/10/EC on the minimum health and safety requirements regarding the exposure of workers to the risks arasing from physical agents (noise) (2003)
  • Sound Advice: Control of noise at Work in music and entertainment – the Health and Safety Executive (2008)
  • E. Hatlevik – Are musicians affected by room acoustics in rehearsal rooms – Master’s Thesis – Norwegian University of Science and Technology NTNU (2012)
  • O. Riduan – Designing small music practice rooms for sound quality – Proceedings – International Congress on Acoustics (2010)
  • C. Pop – Music practice rooms: Ambitions, limitations and practical acoustic design – Proceedings – International Symposium on Music Acoustics (2019)
  • H. Drotleff – New room acoustic design concept for rehearsal rooms – CFA DAGA ’04 , Strasbourg 22-25/03/2004 (2004)
  • H. Koskinen – Facilities for music education and their acoustical design – article – International Journal of Occupational Safety and Ergonomics
  • McCue – Rehearsal room Acoustics, acoustical design of music education facilities – Journal of Acoustical Society of America (1990)
  • Lamberty – Music Practice Rooms – Journal of Sound and Vibration (Vol. 60, No.1)
  • R. Walker – Acoustic Criteria and Specification – BB R&D White paper WHP021 (2002)
  • Skalevik – Rehearsal room acoustics for the orchestra musician – Proceedings – Baltic-Nordic Acoustics Meeting (2014)
  • O’Brien et al. – Nature of orchestral noise – Journal of Acoustic Society of America (2008)
  • G. Leitermann – Theatre Planning – A focal press book (2017)
  • J. Strong – Theatre Buildings – A design guide – Association of british theatre technicians (2010)
  • Norwegian Standard NS 8178:2014 – Acoustic criteria for rooms and spaces for music rehearsal and performance
  • R. Wenmaekers – Stage acoustics sound exposure – www.stageacoustics.wordpress.com/sound-exposure-reduction

Design of music rehearsal rooms – Part 1: The goals for a successful acoustic design

 

When Atelier Crescendo asked Sir James MacMillan about how the quality of the music spaces can contribute to the musical creativity, the music education and the music performance during his interview, he replied:

“It is very important for young musicians to sound good in the early stages of their musical development. If they sound good on their instrument, in their voice, in their choir, in their ensemble, to their peers, to their parents and to the local audience that comes to listen, then the delight of music-making is enhanced. And that delight is part of what motivates a young musician to continue.

So, it is vitally important to get the acoustical design right in an educational setting.”

Sir James MacMillan

Following this comment, it was hard to not write anything about the acoustic design of music rehearsal rooms.  

But the design of such spaces goes beyond the acoustic aspect. So, based on their experience and knowledge, Atelier Crescendo and Ducks Sceno have collaborated on writing a series articles to raise insight on what the design of rehearsal rooms should consider. 

The topic is pretty large for acoustics as there are different types of rehearsal/practice rooms to cover.

Therefore, this series of articles only consider rehearsal spaces for orchestras or ensembles of a ‘standard’ size

 

  what is considered an orchestra/ensemble of a ‘standard’ size? this is a group of musicians that includes:

  • between 12 and 35 musicians.

  • a minimum number or no power amplified instruments.

 

Also, some acoustic aspects have not been treated in this series. They are external noise intrusion, the internal sound insulation, noise and vibration from the building services. If you need some insights about these topics, you can read the following posts:

The first article of the series answers the question What are the goals for a successful acoustic design?

Part 2 provides some acoustic design tips when planning the design of rehearsal spaces. 

Part 3,  written by Ducks Sceno (Theatre Consultants) with contributions from Atelier Crescendo, highlights other general design considerations you should think about for rehearsal rooms

 

What is a successful acoustic design for a music rehearsal room? 

 

successful acoustic design for rehearsal rooms - rehearsal room - musical acoustical acoustics - architectural acoustics - architectural design - performing arts - sound reflection - sound absorption - sound diffusion - acoustic consultant - acoustic engineer - concert halls acoustics - theatre acoustics

You can consider successful the acoustic design of a rehearsal room when you have created a space:

 

  • where musicians can hear themselves and each other.
  • where the music energy is contained to the right level (not too loud but not too quiet either).
  • where musicians enjoy playing and they can prepare them well to perform (this is when the rehearsal space is part of a large performance facility with a main – larger – venue). 

These three aspects are discussed below in more detail.

 

 

A space where musicians can hear themselves and each other 

hearing instruments - hearing the music - successful acoustic design for rehearsal rooms - rehearsal room - musical acoustical acoustics - architectural acoustics - architectural design - performing arts - sound reflection - sound absorption - sound diffusion - acoustic consultant - acoustic engineer - concert halls acoustics - theatre acoustics

Obviously, to hear your own instrument and other instruments, there needs to be a balance between the volume of every instrument. 

To hear your own instrument, its volume needs to be higher (to your ears!) than the volume of the music around you. But not too high either, because you still want to hear the other instruments to play in sync with them.

Also, a good balance would make the quieter or more remote instruments still audible. Whilst the louder and close instruments are attenuated enough, so that their sound doesn’t mask the others. 

 

Note: We are talking about instruments here, but the same applies to voices.

 

But, in an environment with reflective surfaces surrounding you, it’s not just about volume. It is also about the timing!

More exactly, when the sound of your and other instruments, reflected on the surrounding surfaces,  reaches you.  

This is when you get into the science of sound reverberation.

 

Note: if you need a refresher about the basics of sound reverberation, you can read these two posts:

 

When designing an environment for orchestras and ensembles, you need to balance the following:

  • the direct and reflected sound energy of the instruments arriving early to your ears, and ;
  • the reflected sound energy of the instruments arriving late to your ears.   

Generally, the reflected sound energy arriving within the first 100 ms is quite beneficial for the intelligibility and clarity of the musical messages.

 

hearing instruments - hearing the music - successful acoustic design for rehearsal rooms - rehearsal room - musical acoustical acoustics - architectural acoustics - architectural design - performing arts - sound reflection - sound absorption - sound diffusion - acoustic consultant - acoustic engineer - concert halls acoustics - theatre acoustics
Example of sound reverberation in a rehearsal room

Finally, it is particularly important for the musicians to hear musical details such as attack transients. They allow to communicate the rhythm or the musical expressions and are generally emitted at mid and high frequencies.

So it is crucial to keep the direct and reflected sounds at these frequencies as much as possible and absorb some amount of low frequencies.

 

 

A space that contains music energy to the right level containing music sound - successful acoustic design for rehearsal rooms - rehearsal room - musical acoustical acoustics - architectural acoustics - architectural design - performing arts - sound reflection - sound absorption - sound diffusion - acoustic consultant - acoustic engineer - concert halls acoustics - theatre acoustics

Obviously, playing within an orchestra that sounds loud is not comfortable. But the main problem is that it causes hearing loss if it happens regularly

Most of the time, musicians can’t wear ear defenders or ear plugs because they need to be able to hear themselves as well as their fellow musicians. 

An orchestra can sound loud for several reasons:

  • the rehearsal space is just too small for an orchestra.
  • the rehearsal space is too small for the type of orchestra. In other words, there are too many loud instruments (such as percussions, brass instruments, amplified instruments, etc) and the volume of the space is not big enough to accommodate them.
  • some surrounding surfaces reflect too much sound at certain locations. 
  • some hard surfaces are too close. These can be the walls, the balconies or also the overhead reflector(s).  
  • there are too many hard finishes (i.e. sound reflective) and not enough sound absorptive materials.

All or some of the above can lead to a form of Lombart effect (also called cocktail effect). The orchestra is too loud for the musicians to hear themselves. So they play louder. But their neighbours also play louder. And that snowballs throughout the orchestra making it very loud

 

A space where musicians enjoy playing and can prepare them well to perform

musicians enjoying playing music and rehearsing - successful acoustic design for rehearsal rooms - rehearsal room - musical acoustical acoustics - architectural acoustics - architectural design - performing arts - sound reflection - sound absorption - sound diffusion - acoustic consultant - acoustic engineer - concert halls acoustics - theatre acoustics

Sometimes the rehearsal space is part of a large performing arts facility. It can then be used by either the local orchestra or touring orchestras who need to do their final adjustments before the ‘big concert’.

 

  Note: Sometimes, rehearsal spaces are also used as actual performance spaces for smaller audiences.

 

Because every performance venue is acoustically different (this is what makes them unique!), musicians always have to adapt the way they play for the space. Whilst the main performance space might not always be available, the rehearsal should offer an opportunity to know what it is like to play on stage. 

Obviously, this is to a certain degree, because you can’t replicate the exact same acoustic conditions of the stage. At least, musicians should be given a taste.  

 

On a more general point of view, rehearsal spaces should make the musicians ‘feel at home’ as much as possible, whether they are from the local orchestra or a touring orchestra.

It should be a comfortable place (acoustically, visually and physically) where musicians enjoy playing and practicing. So that they are in the best conditions to communicate the emotions of their music. 

So the architectural design should be carefully thought out including:

  • the shape of the finishes and the room itself.
  • the color of the finishes and the furniture within the room.
  • the layout of the room and of the building.
  • the acoustic and the physical flexibility of the room.
  • the access to the rehearsal room from other spaces of the building (such as changing rooms, restaurant, reception, toilets, breakout areas, etc) 

 

References for acoustic design of music rehearsal rooms

The documents and materials reviewed to write this article are presented at the end of Part 2.